Ever since the advent of the first computer, there has been an unending drive to make computers and their components smaller, faster, and more powerful. These goals have created a whole new array of engineering concerns such as making a high number of robust electrical connections in very small spaces as well as providing for near-zero tolerance flatness of component casings. Other concerns include selecting materials to minimize differences in the coefficients of thermal expansion between the different types of conductive and non-conductive materials used in electronic components.
One type of computer-based electronic component is a column grid array integrated circuit package. These packages can be electrically connected and secured to a printed circuit board via an array of solder columns that extend from the integrated circuit package for connection to the printed circuit board. The material and dimensions of these solder column arrays generally accommodate the difference in thermal expansion between the printed circuit board and the integrated circuit package, which contributes to their strong joint reliability.
However, large integrated circuit packages also require large thermal solutions, such as heat sinks, which in turn place significant long-term static compressive loads on the solder columns. Moreover, in order to attach the appropriate sized thermal solution (e.g. heat sink) to the substrate and to insure a good thermal interface between the heat sink and the integrated circuit package, a significant retention load must be place on the package. With a large integrated circuit package, the solder columns cannot bear this long-term static compressive load for very long without exhibiting creep, and ultimately some form of failure mode, such as buckling, bending, and/or solder joint disruption. In particular, any load of more than about 10-20 grams per solder column will exceed the limits of the solder columns. In addition, solder columns experience short-term dynamic loading from shock and vibration during shipping and/or during mobile use. For these reasons, column grid array packages having solder columns arrays have limited application for interconnecting large or high power integrated circuit packages on printed circuit boards.
One attempt at overcoming these issues includes placing non-conductive, rigid column supports underneath the substrate of the integrated circuit packages to help bear the high retention load that is required. The load is translated through the substrate to the rigid column supports, which are positioned side-by-side with the solder columns to help bear the long-term, static compressive load. For example, see U.S. Pat. No. 6,541,710, titled METHOD AND APPARATUS OF SUPPORTING CIRCUIT COMPONENT SOLDER COLUMN ARRAY USING INTERSPERSED RIGID COLUMNS. However, to gain sufficient support from the rigid column supports, the integrated circuit package needs to be slightly larger to accommodate the non-conductive column locations within the contact array. Since space on the printed circuit board is at a premium, larger package sizes are less desirable.
Other attempts at supplementing mechanical support for solder column arrays include setting a shim underneath a portion of the integrated circuit package and using an epoxy adhesive to fix the shim in place relative to the package. Using an epoxy adhesive can be messy, difficult to precisely place, slow due to curing time, and can introduce additional stress and strain issues because the epoxy is fixed relative to the package and the shim. In addition, with an epoxy in place, it becomes difficult to remove the package in the event that reworking of the circuit board becomes necessary. Finally, adding an epoxy adds yet another material parameter to the already delicate task of matching coefficients of thermal expansion between materials of the substrate, solder columns, and printed circuit board.
Accordingly, solder column arrays remain a limiting factor in the size and power of integrated circuit packages that can be used in the column grid array configuration.